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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org,
        syzbot+e73f2fb5ed5a5df36d33@syzkaller.appspotmail.com,
        Chris Wilson <chris@chris-wilson.co.uk>,
        Laura Abbott <labbott@redhat.com>,
        Daniel Vetter <daniel.vetter@ffwll.ch>,
        Eric Biggers <ebiggers@google.com>,
        Rodrigo Siqueira <rodrigosiqueiramelo@gmail.com>,
        Maxime Ripard <maxime.ripard@bootlin.com>
Subject: [PATCH 4.19 097/134] drm/vgem: fix use-after-free when drm_gem_handle_create() fails
Date:   Mon,  1 Apr 2019 19:02:13 +0200
Message-Id: <20190401170053.340382505@linuxfoundation.org>
In-Reply-To: <20190401170044.243719205@linuxfoundation.org>
References: <20190401170044.243719205@linuxfoundation.org>
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4.19-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Eric Biggers <ebiggers@google.com>

commit 21d2b122732318b48c10b7262e15595ce54511d3 upstream.

If drm_gem_handle_create() fails in vgem_gem_create(), then the
drm_vgem_gem_object is freed twice: once when the reference is dropped
by drm_gem_object_put_unlocked(), and again by __vgem_gem_destroy().

This was hit by syzkaller using fault injection.

Fix it by skipping the second free.

Reported-by: syzbot+e73f2fb5ed5a5df36d33@syzkaller.appspotmail.com
Fixes: af33a9190d02 ("drm/vgem: Enable dmabuf import interfaces")
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Laura Abbott <labbott@redhat.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: stable@vger.kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>
Acked-by: Laura Abbott <labbott@redhat.com>
Signed-off-by: Rodrigo Siqueira <rodrigosiqueiramelo@gmail.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190226214451.195123-1-ebiggers@kernel.org
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/gpu/drm/vgem/vgem_drv.c |    6 +-----
 1 file changed, 1 insertion(+), 5 deletions(-)

--- a/drivers/gpu/drm/vgem/vgem_drv.c
+++ b/drivers/gpu/drm/vgem/vgem_drv.c
@@ -191,13 +191,9 @@ static struct drm_gem_object *vgem_gem_c
 	ret = drm_gem_handle_create(file, &obj->base, handle);
 	drm_gem_object_put_unlocked(&obj->base);
 	if (ret)
-		goto err;
+		return ERR_PTR(ret);
 
 	return &obj->base;
-
-err:
-	__vgem_gem_destroy(obj);
-	return ERR_PTR(ret);
 }
 
 static int vgem_gem_dumb_create(struct drm_file *file, struct drm_device *dev,